The purpose of this research is to investigate how historical developments of nurse practitioner legislation are related to their ability to provide primary care to underserved populations. Nursing legislation varies among states in terms of nurse practitioners' ability to practice without direct physician oversight. Since most physicians provide care primarily to insured people in urban or suburban settings, restrictive legislation can limit nurse practitioners' opportunities to provide care to uninsured, underinsured, and vulnerable populations. Conversely, legislation that permits nurse practitioners' autonomous practice may facilitate access to care for these populations. The factors, events, and circumstances instrumental in this process can be identified through an organized analysis of contextual data and events, from 1965 to 1990, that supported the development of legislation endorsing or restricting autonomous advanced nursing practice. Examining the variation in the progression of state legislation, using historical case study methods, could provide an understanding of the complex social and economic factors affecting nurse practitioner practice legislation and its effect on access to primary care service.